The invention relates to an assembly for effecting vertical and rotational displacement of a working member. More particularly the invention concerns the vertical displacement and rotation of a knife assembly or ribbon clamp assembly for securing a ribbon in position and cutting the ribbon. Additionally sensing means are included for positively sensing that the motion of the working member is as desired.
In order to provide a continuous ribbon of material to a process it is sometimes necessary to unwind large rolls of ribbon material. These rolls of ribbon material may be mounted on a chuck assembly and unwound at a desired rate. Upon the termination of one roll it is necessary to join the beginning end of the next roll to be mounted to the chuck assembly to the trail end of the expired roll.
As disclosed in related patent application entitled "Method and Apparatus For Unwinding And Splicing Successive Rolls", Ser. No. 617,992, a paster arm assembly may be utilized to swing up about a pivot point which is also the pivot point for a pulley over which the ribbon is guided. On the paster arm assembly are a ribbon clamp assembly for releasably clamping the ribbon to secure the tension between the clamping point and a dancer downstream therefrom, a vacuum cup for securing the cut end of the ribbon in position for later application of an adhesive and a ribbon knife assembly for selectively cutting the ribbon to provide a trail end from the old roll.
It is necessary that both the ribbon clamp assembly and the ribbon knife assembly have a working member which is positioned so as not to interfere with the orderly unwinding of the ribbon material during unwinding operations. Additionally this working member must be capable of being displaced upwardly to pass over the ribbon when the paster arm has been rotated upwardly in contact with the ribbon and then thereafter be displaced downwardly to either clamp the ribbon between a clamp bar and a clamp pad or to cut the ribbon between a stationary knife blade and a moving knife blade. After the operation has been complete the working member must again be displaced upwardly and rotated back to the starting rotational position. The working member may then be displaced downwardly to its beginning point. Hence it may seen that there must be provided an effective mechanism for controlling the rotational and vertical displacement of the working member.
In order to provide a failsafe system it is desirable to detect that the mechanism has made each motion as required. This provides a safety check to determine that the working member has been displaced either upwardly or downwardly and that the working member has been displaced either between an in or an out position. By positively sensing the position of the working member the successive steps may be sequenced thereafter.